The term epilepsies is a collective designation for a group of central nervous system disorders having in common the repeated occurrence of sudden and transitory episodes of abnormal phenomena of motor, convulsion, sensory, autonomic, or psychic origin. The seizures are nearly always correlated with abnormal and excessive discharges in the brain which can be recorded by an electroencephalogram.
Epilepsy afflicts millions of people worldwide, and the disease is more common in children than in adults. For the purposes of drug treatment, it is useful to classify patients according to the type of seizure the patient experiences. The generally accepted classification of epileptic seizures comprises partial seizures consisting of focal and local seizures, and generalized seizures consisting of convulsive or nonconvulsive seizures. Partial seizures are classified further as simple partial seizures, complex partial seizures, and partial seizures secondarily generalized. Generalized seizures are classified further as absence seizures, atypical absence seizures, myoclonia seizures, clonic seizures, tonic seizures, tonic-clonic and atonic seizures. The epilepsies are presented in The Pharmacological Basis of Therapeutics, 8th Ed, Chapter 19 (1990), Editors Gilman and Rall, Pergamon Press.
Antiepileptic drugs are available for treating epilepsies, as disclosed in Pharmaceutical Sciences, Remington's, 18th Ed., pp 1072-1081 (1990) published by Mack Publishing Co., and while the drugs are useful for treating the epilepsies, there are many shortcomings associated with these drugs. For instance, the drugs often are poorly soluble in aqueous and biological fluids, which property makes it difficult to both provide and dispense the drugs from a dosage form in a known dose over and extended time. The drugs also can be extremely hygroscopic and they may liquify rapidly, which physical-chemical characteristic dictates against their delivery from a dosage form at a controlled rate over a prolonged period of time. Then too, many drugs exhibit a short half-life that can lead to fluctuations in blood antiepileptic drug levels. These properties can interfere with manufacture and the release of the drugs from dosage form and from pharmaceutical compositions; and these shortcomings are serious drawbacks in the management of epilepsies.
Prior to this invention, the prior art administered an antiepileptic drug in conventional forms like a standard nonrate tablet or a common dosedumping capsule at repetitive dosing intervals. The prior art modes of therapy leads to a drug concentration in the blood during the dosing interval, followed by a decrease in drug concentration as a result of drug absorption, distribution, metabolism, and elimination. The concentration difference in dosing intervals is related to the presence and to the absence of administered drug, which is a major disadvantage associated with conventional dosage forms. Conventional dosage forms and their mode of operation are discussed in Pharmaceutical Sciences, Remington, 18th Ed., pp 1676-1686 (1990), Mack Publishing Co.; The Pharmacological and Clinical Pharmacokinetics, 3rd Ed., pp 1-28 (1984), published by Lea & Febiger, Philadelphia, Pa.; and in U.S. Pat. Nos. 3,598,122 and 2,598,123, both issued to Zaffaroni.
The above presentation dictates of the critical need for a dosage form that overcomes the shortcomings of conventional dosage forms, including tablets, capsules, elixirs and suspensions. These conventional dosage forms produce peaks and valley patterns, and they do not provide for dosage-regulated drug therapy over an extended period of time. The drug, as delivered by the prior art is dosed twice or thrice a day, which does not lend itself to controlled and sustained therapy. This prior art pattern of drug administration speaks of the need for a dosage form that can administer the drug in a rate-controlled pattern over an extended time to provide constant therapy and thereby eliminate the peaks and valleys and eliminate the need for multiple uncontrolled dosing of the drug.
The prior art provided controlled-release dosage forms that can administer a drug continuously over time for controlled-rate therapy, as in, for example, U.S. Pat. No. 4,327,725 issued to Cortese and Theeuwes, and in U.S. Pat. Nos. 4,612,008; 4,765,989; and 4,783,337 issued to Wong, Barclay, Deters and Theeuwes. The dosage forms disclosed in these patents provide a controlled-rate drug delivery over an extended time to provide constant drug therapy and thereby eliminate the need for multiple dosing of the drug. These dosage forms can deliver many drugs for their intended therapy, but there are certain drugs that are not readily manufactured and delivered from dosage forms. For example, phenytoin sodium converts to practically insoluble phenytoin in the gastrointestinal pH range of 1 to 8 and the release of unprotected drug in this range is incomplete and this abstracts from acceptable therapy.
It is immediately apparent, in the light of the above presentation, that an urgent need exists for a dosage form endowed with controlled-release delivery for the administration of an antiepileptic drug for antiepileptic therapy. The need exists for this dosage form for delivering an antiepileptic drug in a controlled-sustained dose in a therapeutic antiepileptic range and for simulateously providing extended therapy. It will be appreciated by those versed in the dispensing antiepileptic drug art, that such a dosage form that can administer an antiepileptic drug in a controlled-rate dose over time, and it would be a major advancement in the therapy of the epilepsies.